Power cell having a glass solid electrolyte

ABSTRACT

A power cell having an anode, a cathode and a solid electrolyte is improved by having as the solid electrolyte a glass comprising either (1) from about 22 mole percent to about 47 mole percent Na 2  O, from about 4 mole percent to about 9 mole percent Y 2  O 3  and from about 47 mole percent to about 70 mole percent SiO 2  or (2) from about 34 mole percent to about 47 mole percent Li 2  O, from about 5 mole percent to about 9 mole percent Y 2  O 3  and from about 47 mole percent to about 58 mole percent SiO 2 .

The present invention relates to a power cell and more particularly to apower cell or battery having a glass solid electrolyte.

In view of the fact that glasses can be formed into thin sheets or smalldiameter tubes, a higher electrolyte resistance can be tolerated for apower cell or a battery than is possible with a ceramic electrolyte,while still attaining good energy density. Glasses are also generallysimple to synthesize. These two points have encouraged many researchersto attempt to develop glass solid electrolytes for Na/S power cells orother cells. Such electrolytes must have ionic conductivities of atleast 10⁻⁴ (ohm-cm)⁻¹ at the temperature of use, e.g., 300° C., and becompatible with the chosen anode and cathode materials.

It is the principal object of the present invention to provide a powercell or battery having an improved glass solid electrolyte.

In accordance with a first embodiment of the present invention, a powercell or battery having an anode, a cathode and a solid electrolyte isimproved by having as the solid electrolyte a glass comprising fromabout 22 mole percent to about 47 mole percent Na₂ O, from about 4 molepercent to about 9 mole percent Y₂ O₃ and from about 47 mole percent toabout 70 mole percent SiO₂. Preferably, in this first embodiment theglass solid electrolyte in the power cell or battery comprises about 39mole percent Na₂ O, about 8 mole percent Y₂ O₃ and about 53 mole percentSiO₂.

In accordance with a second embodiment of the present invention, thepower cell or battery having an anode, a cathode and a solid electrolyteis improved by having as the solid electrolyte a glass comprising fromabout 34 mole percent to about 47 mole percent Li₂ O, from about 5 molepercent to about 9 mole percent Y₂ O₃ and from about 47 mole percent toabout 58 mole percent SiO₂. Preferably, in this second embodiment theglass solid electrolyte in the power cell or battery comprises about 47mole percent Li₂ O, about 6 mole percent Y₂ O₃ and about 47 mole percentSiO₂.

The anode and cathode are preferably sodium (Na) and sulfur (S),respectively, in the first embodiment, whereas the anode and cathode arepreferably lithium (Li) and sulfur (S), respectively, in the secondembodiment. However, other conventional electrode materials could beused as the two electrodes.

The improved glass solid electrolytes used in the power cells of thepresent invention were synthesized in accordance with the followingprocedure. Appropriate amounts of Na₂ CO₃ or Li₂ CO₃, Y₂ O₃ and SiO₂were slurry milled in acetone, dried, calcined in alumina crucibles at700° C.-1000° C. for 8 hours to drive off CO₂, then air cooled. Thecalcined material was transferred to a platinum crucible and melted inair at a furnace temperature of 1000° C. to 1600° C., depending on thecomposition. Each melt was held at about 50° C. above the meltingtemperature for one hour to remove gas bubbles, then the crucible wasrapidly removed from the furnace and the liquid poured onto a roomtemperature alumina refractory brick. A radiation shield was placed overthe quenched melts to prevent ultra-rapid surface cooling.

Using the above synthesis procedure, glass solid electrolytes wereprepared having the compositions set forth in Tables I and II below.Their ionic conductivities are also set forth in Tables I and II.

Total (electronic+ionic) conductivities were measured by a standard ACmethod (J. E. Bauerle, J. Phys. Chem. Solids 30, 2657 (1969)). Since theelectronic conductivities of glasses are very small, it was assumed thatthe ionic conductivities set forth in Tables I and II below are equal tothe measured total conductivities.

                  TABLE I                                                         ______________________________________                                                            Ionic                                                                         Conductivity                                              Composition - mole percent                                                                        at 300° C.                                         Na.sub.2 O                                                                             Y.sub.2 O.sub.3                                                                           SiO.sub.2                                                                            (ohm - cm).sup.-1                                 ______________________________________                                        22.16    8.76        69.08  9.77 × 10.sup.-5                            26.85    8.94        64.21  1.55 × 10.sup.-4                            39.12    5.02        55.86  2.14 × 10.sup.-4                            29.01    8.50        62.48  3.76 × 10.sup.-4                            31.65    8.53        59.82  5.03 × 10.sup.-4                            29.27    7.85        62.88  5.69 × 10.sup.-4                            42.69    4.76        52.54  6.64 × 10.sup.-4                            35.05    7.55        57.39  8.91 × 10.sup.-4                            37.92    7.64        54.44  1.18 × 10.sup.-3                            36.22    8.45        55.33  1. 23 × 10.sup.-3                           37.89    8.00        54.11  1.50 × 10.sup.-3                            44.94    4.58        50.48  1.51 × 10.sup.-3                            37.78    5.91        56.31  1.88 × 10.sup.-3                            38.67    4.39        56.94  1.99 × 10.sup.-3                            46.48    5.69        47.83  2.40 × 10.sup.-3                            39.05    7.54        53.40  3.39 × 10.sup.-3                            ______________________________________                                    

                  TABLE II                                                        ______________________________________                                                            Ionic                                                                         Conductivity                                              Composition - mole percent                                                                        at 300° C.                                         Li.sub.2 O                                                                            Y.sub.2 O.sub.3                                                                            SiO.sub.2                                                                            (ohm - cm).sup.-1                                 ______________________________________                                        40.87   6.89         52.24  2.82 × 10.sup.-4                            34.84   7.78         57.38  4.07 × 10.sup.-4                            38.17   8.40         53.43  4.89 × 10.sup.-4                            40.08   5.55         54.37  1.30 × 10.sup.-3                            39.71   6.20         54.09  1.38 × 10.sup.-3                            42.08   5.28         52.63  1.74 × 10.sup.-3                            43.39   5.33         51.28  2.45 × 10.sup.-3                            47      6            47     2.98 × 10.sup.-3                            ______________________________________                                    

The glasses in Tables I and II above were clear and colorless or lightgreen.

From the data in Table I, it will be noted that all the glasses hadionic conductivities between about 1×10⁻⁴ and about 4×10⁻³ (ohm-cm)⁻¹ at300° C., making them acceptable as solid electrolytes for power cellsoperating at that temperature or higher. The highest ionic conductivity,namely, 3.4×10⁻³ (ohm-cm)⁻¹, at 300° C., occurred for the glass formedof about 39 mole percent Na₂ O, about 8 mole percent Y₂ O₃ and about 53mole percent SiO₂. This ionic conductivity is 2.3 times higher than thatrecently reported for the best sodium zirconium phosphosilicate glasssynthesized by Argonne National Laboratory, namely, 1.5×10⁻³ (ohm-cm)⁻¹.(S. Susman, C. J. Delbecq, J. A. Mc. Millan and M. F. Roche, Solid StateIonics 9/10 667 (1983))

Also from the data in Table II above it will be noted that all theglasses had ionic conductivities between about 2×10⁻⁴ and about 3×10-3(ohm-cm)⁻¹ at 300° C., making them acceptable as solid electrolytes forpower cells operating at that temperature or higher. The highest ionicconductivity, namely, 2.98×10⁻³ (ohm-cm)⁻¹ at 300° C., occurred for theglass formed of about 47 mole percent Li₂ O, about 6 mole percent Y₂ O₃and about 47 mole percent SIO₂.

Compatability tests were run on the glass solid electrolytes used in thepower cells of the present invention. Thus, pieces of variouscompositions of the glasses were placed in silica tubes along withelemental sodium (Na) or lithium (Li) or sulfur (S) inside an argonatmosphere glovebox, sealed, removed from the glovebox and heated insidean autoclave at 200° C. and 300° C. The samples were left at thesetemperatures for several days, then removed and examined by scanningelectron microscope (SEM) and energy dispersion analysis. Discolorationof the samples was observed, but examination showed that this was due toa surface coating of sodium or lithium or sulfur on the samples and notto chemical reactions.

The above data on ionic conductivity and compatability show that theglass solid electrolytes are suitable for use in the power cells of thepresent invention, particularly the power cells having a molten sodiumor lithium anode and a molten sulfur cathode.

What is claimed is:
 1. In a power cell having an anode, a cathode and asolid electrolyte, the improvement which comprises said solidelectrolyte is a glass comprising from about 22 mole percent to about 47mole percent Na₂ O, from about 4 mole percent to about 9 mole percent Y₂O₃ and from about 47 mole percent to about 70 mole percent SiO₂.
 2. Apower cell as defined by claim 1 wherein said solid electrolyte is aglass comprising about 39 mole percent Na₂ O, about 8 mole percent Y₂ O₃and about 53 mole percent SiO₂.
 3. In a power cell having an anode, acathode and a solid electrolyte, the improvement which comprises saidsolid electrolyte is a glass comprising from about 34 mole percent toabout 47 mole percent Li₂ O, from about 5 mole percent to about 9 molepercent Y₂)₃ and from about 47 mole percent to about 58 mole percentSiO₂.
 4. A power cell as defined by claim 3 wherein said solidelectrolyte is a glass comprising about 47 mole percent Li₂ O, about 6mole percent Y₂ O₃ and about 47 mole percent SiO₂.
 5. A power cellcomprising a sodium anode, a sulfur cathode and a glass solidelectrolyte formed of from about 22 mole percent to about 47 molepercent Na₂ O, from about 4 mole percent to about 9 mole percent Y₂ O₃and from about 47 mole percent to about 70 mole percent SiO₂.
 6. A powercell as defined by claim 5 wherein said glass solid electrolyte isformed of about 39 mole percent Na₂ O, about 8 mole percent Y₂ O₃ andabout 53 mole percent SiO₂.
 7. A power cell comprising a lithium anode,a sulfur cathode and a glass solid electrolyte formed of from about 34mole percent to about 47 mole percent Li₂ O, from about 5 mole percentto about 9 mole percent Y₂ O₃ and from about 47 mole percent to about 58mole percent SiO₂.
 8. A power cell as defined by claim 7 wherein saidglass solid electrolyte is formed of about 47 mole percent Li₂ O about 6mole percent Y₂ O₃ and about 47 mole percent SiO₂.